1. Field of the Invention
The present invention relates to a fast atom beam source used for sputtering and the like.
2. Prior Art
Atoms or molecules subject to thermal kinetics in a normal atmosphere have kinetic energy of approximately 0.05 eV. Molecules or atoms moving with kinetic energy remarkably higher than that level are generally known as "fast atoms" and if they flow in one direction as a beam, the beam is called as "a fast atom beam".
Sputtering technology by energetic beam bombardment has been used in sputter etching or material composition analysis. In the technology, an energetic ion beam or a fast atom beam is used as the energetic beam for bombardment.
As a source for a fast atom beam, some apparatuses convert ions emitted from an ion source into fast atoms by neutralization with ion-electron recombination and the other apparatuses emit a fast atom beam directly as shown in FIG. 4.
Concerning the construction of an usual source for a fast atom beam shown in FIG. 4, a doughnut-shaped anode 2 is set at the center of a cylindrical cathode 1. The cathode 1 and the anode 2 are connected to a DC high voltage power supply 3 arranged outside a vacuum vessel. Oxygen gas, for example, is let in through a gas nozzle 4 opening into the inside of the cylindrical cathode 1 and plasma 6 due to gas discharge is generated in the cylindrical cathode 1 by impressing supplying of DC high voltage through the DC high voltage power supply 3, thereby oxygen ions and electrons are produced. Furthermore, the electrons emitted from the cathode 1 are forced to oscillate in high frequency across the anode 2 and produce many oxygen ions by collision with the oxygen gas.
The oxygen ions produced in plasma are accelerated towards the bottom of the cylindrical cathode 1. Then, oxygen ions return to oxygen atoms by neutralization through contact with oxygen gas molecules and by recombination with electrons remaining near the cathode 1.
As a kinetic energy loss through contact with gas molecules and electrons is small, the kinetic energy of the oxygen ions is directly received to the oxygen atoms. Thus fast atoms are born. The fast atoms are emitted as a fast atom beam 8 from the emission orifices 7 provided on the bottom of the cylindrical cathode 1.
A fast atom beam without electric charges may be used for processing or analysis not only for metals and semiconductors but also for plastics and ceramics, etc. to which the workability for an ion beam is poor.
In the above-mentioned fast atom beam source, however, the gas should always be supplied to the apparatus in order to make up the material emitted as a fast atom beam.
Therefore, it is required to provide a device for supplying the gas from the outside of the vacuum vessel, and the apparatus will be of a large size.
In addition, it is not desirable for a high vacuum equipment to let in some gas. Further, it will be required to provide some devices for adjusting the feed rate of the gas in order to keep a discharge condition in the fast atom beam source.